Field of the Invention
The present invention relates to peptide agonists of the calcitonin/calcitonin gene-related peptide (CT/CGRP) family of peptide hormones and therapeutic uses thereof.
Description of the Related Art
The CT/CGRP peptide family includes calcitonin gene-related peptide (CGRP), adrenomedullin (ADM), intermedin (IM), calcitonin (CT) and amylin. The biological actions of these peptides are mediated via binding to two closely related type II G protein-coupled receptors, the calcitonin receptor (CTR) and the calcitonin receptor-like receptor (CRLR) (Christopoulos, et al. 1999, Mol. Pharmacol. 56:235-242; Poyner et al. 2002 Pharmacol. Rev. 54:233-246). Although the calcitonin receptor is the main mediator for calcitonin action, it preferentially binds amylin, when the receptor is associated with a receptor activity modifying protein (RAMP) (see, e.g., Tilikaratne, et al. 2000, J. Pharmacol, Exp. Ther. 294(1):61-72). Cloning and functional studies have shown that CGRP, ADM, IM and, to a lesser extent, amylin likewise interact with different combinations of CRLR and the three receptor activity modifying proteins (RAMP-1, RAMP-2 and RAMP-3); see, e.g., McLatchie et al. 1998, Nature 393:333-339 and Roh et al. 2004, JBC 279(8):7264-7274), In fact, co-expression of the calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMPs) is required to generate functional receptors for calcitonin gene-related peptide (CGRP), adrenomedullin (ADM) and intermedin (IM). The formation of heterodimers between RAMPs and CRLR is essential for the proper cell surface targeting and pharmacological characteristics of CGRP, ADM and IM receptors. Co-expression of RAMP-1 with CRLR leads to the formation of a CGRP receptor, whereas RAMP-2 and RAMP-3 co-expression with CRLR form ADM and IM receptors respectively (Miret, et al. 2002, JBC 277(9):6881-6887.) IM has been shown to be a nonselective agonist for all three RAMP/CRLR co-receptors.
The physiological functions of the hormone peptides in the CT/CGRP family are determined by receptor-binding specificity and the tissue expression profiles of individual ligands and their respective receptors and have been shown to be involved in cardiovascular morphogenesis, sensory neurotransmission, inflammatory reactions, nociceptive behavior and glucose homeostasis (see, e.g., Hay, et al. 2001, Trends Pharmacol, Sci, 22:57-59; Shindo, et al. 2001, Circulation 104:1964-1971; Zhang et al. 2001, Pain 89:265-273; Salmon et al. (1999) Neuroreport 10:849-854; Salmon, et al. 2001, Nat. Neurosci. 4: 357-358; and Mulder, et al. 2000, Am. J. Physiol. 278:E684-E691).
Calcitonin gene-related peptide (CGRP) is a peptide which, in several species, exists in two forms, designated CGRP-alpha and CGRP-beta (or CGRP-1 and CGRP-11, respectively). CGRP peptides are highly conserved across species, for example, human and rat CGRP-alpha peptides share 89% amino acid homology (the mature peptides differing by four amino acids) compared to 92% amino acid homology between human alpha- and beta-CGRP (which differ by 3 amino acids). (See for example, Ma, H. 2004, Nature and Science 2(3):41-47.) A well-studied peptide in the CT/CGRP family of peptide hormones, CGRP is a 37 amino acid vasoactive neuropeptide that is released from sensory, motor and enteric nerves comprising an amphiphilic α-helical secondary structure in the amino acid sequence between residues 8-25. CGRP has potent vasodilatory and cardiotonic action, as described, for example, in U.S. Pat. No. 4,530,838 to Evans, et al. CGRP is present in both the central and peripheral nervous systems and is concentrated in those areas of the body receiving sensory input from the dorsal horn with limited amounts associated with autonomic input. In the brain, the peptide is present in the nuclei of sensory and motor cranial nerves and in cell bodies in the hypothalamus, preoptic area, ventromedial thalamus, hippocampus, and the like (Poyner, D. 1992, Pharmac. Ther. 56:23-51).
CGRP is known to be involved in various pharmacological effects, such as: 1) vasodilation, 2) muscle and liver AMP kinase (AMPK) activation and lipolysis and/or fat oxidation, 3) reduction in food intake, 4) inhibition of gastric emptying and modification of gut function and 5) increased glycolysis and inhibition of glycogen synthesis. The net physiological significance of these effects is not completely understood; however, evidence of CGRP's role in fatty acid oxidation and regulation of lipid availability and utilization has been demonstrated (Danaher, et al. 2008 Endocrinology 149(1):154-160). Studies have demonstrated CGRP's role in inhibition of food intake including evidence that its action is via the paraventricular nucleus (PVN) of the hypothalamus. (See for example, Martinez-Alvarez, R M, et al. 2009 Peptides 30(4):803-807 and Dhillo, W. S, et al. 2002, Endocrine Abstracts 3OC43; ISSN1470-3947.) Additionally, it has been shown that CGRP stimulate GLP-1 secretion, a protein known to play an important role in amelioration of diabetes.
Metabolic syndrome is a disease state manifested by obesity, insulin resistance, dyslipidemia and hypertension. Today, these four manifestations are treated by selective treatment paradigms. Native CGRP has a half-life of less than 30 minutes, and a short duration of pharmacological actions after CGRP infusions is evident. Due to vasodilatory effects of administered CGRP, in vivo pharmacological studies of native CGRP can be difficult due to the secondary effects of vasodilation and compensatory vasoconstrictive actions. Thus, the pharmacological usefulness of CGRP, particularly with respect to long-term or chronic use thereof, requires the generation of CGRP analogues with prolonged action and some effects may even only be obtained with longer-acting analogues. Similarly, to be viable as a therapeutic agent, particularly for chronic use, analogues having prolonged action are desirable.